This book constitutes the refereed proceedings of the 9th International Symposium on Search-Based Software Engineering, SSBSE 2017, held in Paderborn, Germany, in September 2017.  The 7 full papers and 5 short papers presented together with 4 challenge track and 2 students student track papers were carefully reviewed and selected from 26 submissions. SSBSE welcomes not only applications from throughout the software engineering lifecycle but also a broad range of search methods ranging from exact Operational Research techniques to nature-inspired algorithms and simulated annealing.